Na K ATPase is an essential enzyme for the vectorial transport of Na across transporting epithelia. ln kidney, digestive tract and exocrine glands, Na K ATPase is localized in the basolateral plasma membrane, while in retinal pigmentary epithelium it is found in the apical plasmalemma. We propose to study the molecular basis of this differential tissue localization at the protein and mRNA levels. Rat kidney, intestinal and RPE Na K ATPase will be localized on semithin frozen sections by immunofluorescence using monospecific rabbit antibodies against alpha and beta subunits. The same antibodies will be used to compare the mobility of alpha and beta subunits from these tissues by Western blot analysis. Peptide maps of alpha and beta subunits (including deglycosylated beta subunit) from the three tissues will be compared in order to search for tissue-specific differences. Finally, the mRNAs for alpha and beta subunits in kidney, intestine and RPE will be compared by Northern blot analysis and Sl mapping techniques using cDNAs coding for rat brain alpha and beta subunits. It is expected that these studies will provide important information leading to the, elucidation of the molecular information responsible for the sorting of apical and basolateral proteins in epithelial cells.